Device for combined detection of axle acceleration and wheel rotational speed and method for determining pressure

ABSTRACT

The pressure in a motor vehicle tire can be determined by means of a ‘wheel-independent’ device ( 1 ) that is in a largely rigid manner connected mechanically to an element ( 2 ) of the vehicle body ( 3, 14 ) oscillating with the motor vehicle wheel ( 4 ).  
     In order to determine the—preferably absolute—tire pressure by combining the evaluation of rotational speed data and axle frequency analysis, said device ( 1 ) includes a signal pre-processing element ( 6 ) provided with electronic components for processing the sensor signals, said element being connected to a magnetic sensor element ( 7 ) and an acceleration sensor element ( 8 ) or to a combined magnetic/acceleration sensor element ( 5 ) by means of an electrically conductive element connection ( 9 ), wherein the magnetic sensor element ( 7 ) or the magnetic/acceleration sensor element ( 5 ) is operatively connected to a magnetic encoder ( 16 ) arranged on the wheel side.  
     To improve determination of characteristic quantities, preferably the vibration behavior of at least two wheels ( 4 ) is analyzed.

BACKGROUND OF THE INVENTION

The present invention relates to a device for the combined detection ofthe axle acceleration and the wheel speed, wherein the device ismechanically connectable to an element of the motor vehicle chassis thatresonates with one motor vehicle wheel respectively as well as a methodof determining the pressure in a motor vehicle tire by means of awheel-speed based method which assesses the tire pressure loss (DDS) byevaluating wheel speed data from several wheel speed sensors andproducing quantities of the ratio between wheel speed data of differentwheel pairs while taking into account data about the current drivingcondition.

Methods for monitoring the tire pressure or determining the tirepressure are known in the art, e.g. from DE-A-197 21 480, wherein a tirepressure loss can be calculated by evaluating a long-term runningbehavior of the individual motor vehicle wheels without the assistanceof pressure sensors. Corresponding methods are used in motor vehiclese.g. under the name ‘DDS’ (Deflation Detection System). On account ofthe indirect measuring method, which is essentially based on theevaluation of wheel speed data, a DDS method is required to detect asreliably as possible disturbances affecting the tires' rotational speedcaused by cornering, acceleration, slowing down, tire exchange, etc.,and to correct the wheel speed data obtained in order to eliminate theeffects of these quantities.

The quality of pressure loss detection depends, among others, on howprecisely specific driving conditions can be detected. Alreadyvibrations of the wheel axle have been detected and processed byacceleration sensors to improve pressure loss detection.

DE 38 09 886 discloses a wheel speed sensor comprising an accelerationsensor in addition to a wheel speed sensor. However, the sensorassemblies described are sophisticated in manufacture and need muchmounting space.

Besides, high-quality wheel speed sensor modules in chip technology arerequired to precisely acquire wheel speed data, as described for examplein German patent application P 44 45 120 or in DE-A-199 22 672. Thedescribed wheel speed sensor modules comprise a magnetized encoderrotating with the wheel and scanned by an active magnetic sensorelement. The acquired wheel speed data is sent by way of a currentinterface to an integrated brake control unit that is appropriate forABS, ESP, and the DDS described hereinabove.

On the other hand, there is the requirement of improving the drivingperformance and driving comfort by actively controlled wheel dampersystems. Acceleration sensors in the area of the wheel axle arenecessary for these actively controlled damper systems. An axlefrequency analysis can be executed on the basis of the axle vibrationssensed by axle acceleration sensors of this type.

An object of the present invention is to determine the—preferablyabsolute—tire pressure by a combined evaluation of wheel speedinformation and axle frequency analysis. An integrated wheel modulesensor unit shall be provided for this purpose, which combinesacceleration sensors and wheel speed sensors to form a tuned totalmodule.

This object is achieved by a device that includes a signalpre-processing element with electronic components for the pre-processingof sensor signals, which is connected to a magnetic sensor element andan acceleration sensor element or a combined magnetic/accelerationsensor element by means of electrically conductive element connections,and wherein the magnetic sensor element or the magnetic/accelerationsensor element is in operative engagement with a wheel-sided magneticencoder, possibly in connection with a method that uses data about thevibration behavior of at least one of the wheels (4), being acquired bymeans of an acceleration sensor (8), with the aid of specific tireparameters for improving the determination of parameters.

The invention discloses a ‘wheel-independent’ tire pressure indicationsystem on the basis of the rotational wheel-speed based ‘DDS’ known inthe art.

The mere wheel speed data according to DDS permit indicating merely thepressure differences of the tire fill pressure of two wheels in eachcase.

The additional data necessary for an exact and absolute‘wheel-independent’ tire pressure indication is obtained by means of anaxle frequency analysis performed complementarily.

When the axle frequency analysis is performed only on one vehicle wheel,the input of specific tire parameters is necessary for a determinationof the absolute pneumatic pressure.

When an axle frequency analysis is performed on at least two vehiclewheels, the parameters necessary for an absolute tire pressuredetermination can be established directly by means of the combinedevaluation of DDS and axle frequency data.

That means: absolute tire pressure values are determined according tothe present invention without the need for mounting battery-poweredsensor modules into the wheels.

Because the range of relevant resonant tire frequencies is reasonablyknown, it is unnecessary to perform a complete Fourier analysis for theaxle frequency analysis. It is fully sufficient to purposefully analyzeonly individual Fourier elements of the axle vibration. This will allowminimizing the calculating effort for the axle frequency analysis to atechnically justifiable extent.

The determination of the tire properties by means of accelerationsensors on the wheel axle affords the advantage that only definedself-movements of the tire are transferred to the wheel axle. Thisfiltering effect considerably simplifies the frequency analysis.

According to the invention, wheel speed sensor and acceleration sensor,preferably combined in a joint device, are coupled to the wheel axle ina mechanically stiff manner.

The method of the invention and the device of the invention can be usedin motor vehicles, which also comprise commercial vehicles and passengercars.

The device of the invention, among others, provides the advantage that ajoint use of the interface and the necessary current supply in additionto low-cost manufacture is possible. Also, the reliability of the totalsystem is enhanced by the integration into a joint housing sealedagainst environmental influences.

Further, the device of the invention can be used to realize anintegrated control system within the integrated brake control unit,which performs the functions DDS, ABS, ESP, etc. performed already in aper se known fashion, in combination with a suspension control in ajoint electronic control unit.

Further, advantages result with respect to a DDS method implementedbecause the additionally existing axle acceleration data can be used toimprove DDS. The data of the DDS system and of the axle frequencyanalysis are not directly correlated. In addition, the functionaldependencies of the DDS and axle frequency data of speed, wheel load,cornering, etc. are distinctly different. Thus, the related wider datarange also leads to a higher rate of safety in the tire pressure controlalarm in total. In principle, problematic driving conditions may thus beidentified reliably, for example, for the rotational-speed basedpressure loss detection, e.g. when tire wear prevails or when the motorvehicle is driven on extremely rough roads.

In a preferred embodiment of the invention, the per se known DDS methodis extended in that the vibration behavior of the wheels is monitoredand stored for a long period of time, and it is possible to reduce therequired memory locations by data compression or data filtering.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1 shows an example for the installation of a device of theinvention on a vibrating element.

FIG. 2 is a view of a device of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The embodiment of FIG. 1 schematically illustrates a wheel suspension 3connected to the vehicle body 14 by way of a spring element 15, and awheel 4 comprising tire, wheel rim and wheel bearing 18 is connected tosaid wheel suspension 3 in an oscillatory manner. A combination sensor 1comprising a magnetic sensor element 7 and an acceleration sensor 8 issecured to the wheel suspension 3 in a mechanically stiff manner by wayof a fastening element 2. As an acceleration sensor 8, e.g. per se knownmicro-mechanical sensors can be used which are etched into a siliconsubstrate, for example. When using micro-mechanical accelerationsensors, it is possible and preferred to integrate the accelerationsensor into the chip of the signal pre-processing unit. Referencenumeral ‘16’ designates an encoder co-rotating with the wheel 4.

FIG. 2 is also a schematic view of a sensor assembly made up of amagnetized encoder 16 co-rotating with wheel 4 and magnetically coupledto the combination sensor element 1 through an air slot. Magnetic sensorelement 7 detects the magnetic field of the encoder 16 by way of amagneto-resistive bridge circuit. The electric signals of the magneticsensor element 7 are sent to an electronic conditioning circuit in aseparately cased chip element 6. Similarly, electric signals of anacceleration sensor element 8 are additionally sent to the conditioningcircuit. The sensor signals processed by the conditioning circuit arethen sent to an electronic brake control unit (ECU) 13 by way ofelectric conduits 17. Normally, each motor vehicle wheel 4 is equippedwith a sensor 1 according to FIG. 2 a. The signal lines of the othersensor elements led to the control unit 13, are not shown. Preferably,the interface between sensor element 1 and ECU 13 is a currentinterface, with two or three wires, and the sensor signals aretransmitted in coded form, preferably by means of pulse-shaped signals.Partial image b) depicts an embodiment in which the acceleration sensor8, for the purpose of saving mounting space, is bent at the electricconnection 9′ between the acceleration sensor element 8 and the signalconditioning element 6 for forming a sandwich-shaped block.

LIST OF REFERENCE NUMERALS

-   1 combination sensor, sensor-   2 fastening element-   3 wheel suspension-   4 wheel-   5 combined magnetic/acceleration sensor-   6 chip element, signal processing element-   7 magnetic sensor element, wheel speed sensor-   8 acceleration sensor, acceleration element-   9,9′ electric connection (between 6 and 8)-   10 lead frame-   11 chip housing-   12 embedding mass-   13 brake control unit (ECU), control unit-   14 vehicle body-   15 spring element-   16 (magnetic) encoder-   17 electric conduits-   18 wheel bearing

1-20. Canceled
 21. A device (1) for the combined detection of the axleacceleration and the wheel speed, wherein the device (1) is mechanicallyconnectable to an element (2) of the motor vehicle chassis (3, 14) thatresonates with one motor vehicle wheel (4) respectively, wherein thedevice comprises a signal pre-processing element (6) with electroniccomponents for the pre-processing of sensor signals, which is connectedto a magnetic sensor element (7) and an acceleration sensor element (8)or a combined magnetic/acceleration sensor element (5) by means ofelectrically conductive element connections (9), and wherein themagnetic sensor element (7) or the magnetic/acceleration sensor element(5) is in operative engagement with a wheel-sided magnetic encoder (16).22. The device according to claim 21, wherein the acceleration sensorelement (8) is integrated in the housing of the signal pre-processingelement (6). 2a. The device according to claim 22, wherein anacceleration sensor element (8) is integrated on the same chip of thecomponents for pre-processing element (6).
 23. The device as claimed inclaim 22, wherein the signal pre-processing element (6), magnetic sensorelement (7) and acceleration sensor element (8) are arranged in a chiphousing (11), with said chip housing (11) being encompassed by a commonembedding mass (12) for protection against circumferential influences.24. The device as claimed in claim 21, comprising connections (9) amongits elements that constitute part of a common lead frame (10).
 25. Thedevice as claimed in claim 21, wherein the acceleration sensor element(8) and the signal pre-processing element (6) are arranged in sandwichconstruction, and the element connections (9′) between the accelerationsensor element (8) and the signal pre-processing element (6) take acurved course.
 26. A method of determining the pressure in a motorvehicle tire by means of a wheel-speed based method which assesses thetire pressure loss (DDS) by evaluating wheel speed data from severalwheel speed sensors and producing quantities of the ratio between wheelspeed data of different wheel pairs while taking into account data aboutthe current driving condition, wherein the method uses data about thevibration behavior of at least one of the wheels (4), being acquired bymeans of an acceleration sensor (8), with the aid of specific tireparameters for improving the determination of parameters.
 27. The methodaccording to claim 26, wherein the method uses data about the vibrationbehavior of at least two wheels (4), wherein at least a part of thespecific tire parameters required for determining absolute tirepressures and the type of tire are found out directly by a linkedevaluation of data of a wheel-speed based pressure loss detection and ofdata from an axle frequency analysis.
 28. The method as claimed in claim7, wherein wheels (4) of different axles are selected for the axlefrequency analysis that is to be performed on at least two wheels (4),and the wheels (4) can have different dimensions.
 29. The method asclaimed in claim 26, utilizing acceleration sensors (8) and wheel speedsensors (7) being configured configured as a device for the combineddetection of axle acceleration and wheel speed.
 30. The method asclaimed in claim 26, wherein the ratios of wheel radii are determined bythe evaluation of wheel speed sensor signals.
 31. The method as claimedin claim 26, wherein the tire pressures are determined by the evaluationof wheel speed data of all wheel positions and the axle vibrations on atleast two wheel positions.
 32. The method as claimed in claim 26,wherein a pre-selection is executed in the axle frequency analysis insuch a fashion that axle vibration is suppressed and only the frequencyrange of a tire's natural vibration (pendulum oscillation) is filteredout of the respective spectra, being dependent on the type of pressureand tire.
 33. The method as claimed in claim 26, wherein the parametersare relative tire pressure values and the improved determinationinvolves that relative tire pressure values are replaced by absolutetire pressure values which inhere a defined rate of uncertainty.
 34. Themethod as claimed in claim 12, wherein influences of wheel load andspeed on the natural frequency of the pendulum oscillation are takeninto account in calculations.
 35. The method as claimed in claim 26,wherein the tire pressure variations caused by changes in speed anddifferent allotments of brake force and driving power are used todetermine tire-related parameters.
 36. The method as claimed in claim26, wherein a predefined pneumatic pressure for a tire is adjusted bymeans of a ‘reset button’ at the control unit.
 37. The method as claimedin claim 26, wherein an absolute tire pressure is determined for eachindividual wheel and indicated on a display device.
 38. The method asclaimed in claim 26, wherein the method is executed in an integratedbrake control unit (13) by a digital computing unit.
 39. The method asclaimed in claim 26, wherein an exact value of the tire pressure isobtained by a statistic averaging operation of several wheel radii andaxle frequency data.
 40. The method as claimed in claim 26, wherein thetire-related parameters are continuously corrected by adjustment of DDSand axle frequency analysis data, and operational changes of the tires.